1. Field of the Invention
The present invention relates to a ceramic matrix composite obtained by combining ceramic fibers with a silicon carbide (SiC) matrix and to a method of manufacturing the same and, more particularly, to a ceramic matrix composite having high strength even in a high-temperature range at, especially, 1,400.degree. C. or higher and a method of manufacturing the same.
2. Description of the Related Art
In general, a ceramic sintered body has strength which is less degraded up to a high temperature, and is more excellent than a conventional metal material in hardness, electric insulating properties, abrasion resistance, heat resistance, corrosion resistance, light-weight properties, and the like. For this reason, the ceramic sintered body is popularly used in a large field as an electronic material or a structure material such as a heavy electric equipment part, an aircraft part, an automobile part, an electronic equipment, a precision instrument, or a semiconductor device material.
However, the ceramic sintered body is easily affected by tensile stress rather than compression stress, and, especially, the ceramic sintered body is broken by the tensile stress at once. That is, the ceramic sintered body disadvantageously has so-called high brittleness. For this reason, in order to make it possible to apply a ceramic part to a portion whose reliability should be high, high toughness of the ceramic sintered body or an increase in fracture energy are strongly demanded.
More specifically, a ceramic structure part used as a gas turbine part, an aircraft part, an automobile part, or the like requires high heat resistance, high refractory, and high reliability. In order to reply to this demand, studies for realizing the following ceramic composite material have advanced in domestic and foreign laboratories. That is, ceramic matrix composites (CMC) are improved on a toughness value or a fracture energy value in such a manner that reinforcements (strengthening materials) such as reinforcement fibers, whiskers, blades, and particles which consist of an inorganic material or a metal are dispersed in a matrix sintered body to be combined with each other.
Among the above ceramic matrix composites (CMC), a ceramic matrix composite using fibers as reinforcements is is excellent in fracture toughness or an increase in fracture energy, and has a great effect for improvement on reliability. As the reinforcement for the CMC, continuous fibers or short fibers such as glass fibers, carbon fibers, or ceramic fibers are mainly used.
Among the ceramic matrix composites which are reinforced or strengthened by fibers, a composite having silicon carbide (SiC) as a matrix is hopeful as a material constituting a structure member for high temperature because the composite has high heat resistance and high oxidation resistance.
Conventionally, as a method of combining reinforcements in the above ceramic matrix composite, the following method is employed. That is, a ceramic material powder is filled in a preform such as a fabric consisting of ceramic fibers by a wet method such as a slip cast method to manufacture a preliminary green body containing reinforcements. As in a conventional method of manufacturing a sintered body, the green body is sintered by atmospheric-pressure sintering, atmosphere pressing sintering, hot press, HIP, or the like.
On the other hand, when a matrix is formed by a reaction-sintering method, a material slurry containing carbon and SiC is impregnated in a preform such as a fabric consisting of ceramic fibers to form a preliminary green body, and reaction-sintering is performed while melted silicon (Si) is impregnated in the preliminary green body to cause the carbon component and melted Si to react with each other. A matrix consisting of a reaction-sintering SiC sintered body is integrally formed to manufacture a composite.
The reaction-sintering SiC sintered body manufactured as described above is rarely contracted during sintering, exhibits high dimensional precision, and has an advantage that a sintered body having a high density can be obtained under the heat condition at a relatively low sintering temperature of about 1,450.degree. C. Furthermore, the reaction-sintering SiC can cope with a complex shape, and has the manufacturing cost which is considerably lower than that of another manufacturing process. For this reason, practical use of the reaction-sintering SiC as a matrix constituent material of a ceramic matrix composite is expected.
However, in a ceramic matrix composite using a reaction-sintering SiC as a matrix, a manufacturing process for impregnating melted Si is employed. For this reason, the reaction-sintering SiC contains 15 to 30% by volume of free Si, and the free Si disadvantageously degrades the high-temperature strength of the composite. More specifically, since the melting point of free Si is relatively low, i.e., 1,410.degree. C., the structural strength of the composite is sharply degraded because of softening and melting of free Si under the high-temperature use condition at 1,400.degree. C. or higher. Therefore, there is a severe problem that the reaction-sintering SiC cannot be used as a structure part material.